From 690038a3c75463681c2acc49689f0472b1698e89 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 23 Mar 2018 06:50:58 -0700
Subject: vm: change encoding of getv, setv and related.

In most compiler uses of bindv, getv and setv,
the operand which names the dynamic symbol is the data table:
a d0-dff register. The source or destination register of the
transfer could be anything. Therefore, the existing encoding
is suboptimal: the symbol is being put into the full sized
operand field of the instruction, and the source or
destination register into the small, ten-bit extra field
in the upper half. This breaks on cases like (set x y)
where x is a deeply nested lexical variable and y is
a dynamic variable. Let's reverse the encoding.

* share/txr/stdlib/asm.tl (op-getv, op-setv): Reverse the
operands. All derived opcodes follow this since they
reuse the code via inheritance.

* vm.c (vm_get_binding): Fetch the symbol from the small
operand field rather than the main operand field.
(vm_getsym, vm_getbind, vm_setsym, vm_bindv): Pull the
destination or source from the main operand of the instruction
rather than the small opreand.
---
 vm.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

(limited to 'vm.c')

diff --git a/vm.c b/vm.c
index 9f0ff266..3b9c64ca 100644
--- a/vm.c
+++ b/vm.c
@@ -707,7 +707,7 @@ static val vm_get_binding(struct vm *vm, vm_word_t insn,
                           val (*lookup_fn)(val env, val sym),
                           val kind_str)
 {
-  val sym = vm_get(vm->dspl, vm_insn_operand(insn));
+  val sym = vm_get(vm->dspl, vm_insn_extra(insn));
   val binding = lookup_fn(nil, sym);
 
   if (nilp(binding))
@@ -721,7 +721,7 @@ static void vm_getsym(struct vm *vm, vm_word_t insn,
                       val kind_str)
 {
   val binding = vm_get_binding(vm, insn, lookup_fn, kind_str);
-  int dst = vm_insn_extra(insn);
+  unsigned dst = vm_insn_operand(insn);
   vm_set(vm->dspl, dst, cdr(binding));
 }
 
@@ -730,7 +730,7 @@ static void vm_getbind(struct vm *vm, vm_word_t insn,
                        val kind_str)
 {
   val binding = vm_get_binding(vm, insn, lookup_fn, kind_str);
-  int dst = vm_insn_extra(insn);
+  unsigned dst = vm_insn_operand(insn);
   vm_set(vm->dspl, dst, binding);
 }
 
@@ -739,14 +739,14 @@ static void vm_setsym(struct vm *vm, vm_word_t insn,
                       val kind_str)
 {
   val binding = vm_get_binding(vm, insn, lookup_fn, kind_str);
-  int src = vm_insn_extra(insn);
+  unsigned src = vm_insn_operand(insn);
   rplacd(binding, vm_get(vm->dspl, src));
 }
 
 static void vm_bindv(struct vm *vm, vm_word_t insn)
 {
-  val sym = vm_get(vm->dspl, vm_insn_operand(insn));
-  int src = vm_insn_extra(insn);
+  val sym = vm_get(vm->dspl, vm_insn_extra(insn));
+  int src = vm_insn_operand(insn);
 
   if (nilp(dyn_env))
     eval_error(vm->vd->bytecode,
-- 
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